The effect of hot liquid water treatment on the properties and catalytic activity of MWW zeolites with various layered structures
Abstract
The properties and catalytic activity of zeolite MWW were investigated before and after water treatment at 160 degrees C for 48 h to evaluate its possible behavior and usefulness in biomass conversion. Four different forms of the MWW zeolite were studied along with a sample of commercial zeolite beta for comparison: MCM-22, MCM49, MCM-56 and Ce/MCM-22.
The treated MWW zeolites showed lesser impact of the exposure to water than the tested zeolite beta. X-ray powder diffraction indicated negligible structural degradation.
Al-27 NMR and FTIR showed reduction of the acid site concentration, while micropore volume decreased by up to 50% as determined by nitrogen sorption. All MWW samples showed high catalytic activity in the reaction of n-propanol with 3,4-dihydro- 2H-pyran (DHP).
Similar reactions between tert-butanol and DHP also showed better activity and relatively small effect of the water treatment for the MWW materials with the exception of the Ce/MCM-22. The latter and the reference zeolite beta showed about 3 times lower conversion.
Ce/MCM-22 was the only sample showing no decrease in acid site concentration as the result of aging in hot water so its lower activity was surprising. We propose that larger size of Ce may be responsible for blocking or otherwise affecting accessibility of the active sites.
The study shows that MWW zeolites may show higher activity than zeolite beta. Incorporation of Ce improves stability of acid centers and although overall performance diminishes it leaves room for improvement, possibly by expanding the interlayer structure.